High-nitrogen austenitic stainless steel

ABSTRACT

A high-nitrogen austenitic stainless steel, containing 0.005 mass %≦C≦0.25 mass %; 15.0 mass %≦Cr≦35.0 mass %; 0.2 mass %&lt;Mn&lt;10.0 mass %; 0.05 mass %≦Mo≦8.0 mass %; 0.01 mass %≦Cu≦4.0 mass %; 0.01 mass %≦Ni&lt;5.0 mass %; 0.8 mass %&lt;N≦1.8 mass %; Si≦2.0 mass %; P≦0.03 mass %; S≦0.05 mass %; Al≦0.030 mass %; 0≦0.020 mass %, and the balance substantially including Fe and impurities, and having a PRE (=(Cr+3.3Mo+16N)/Mn (mass %)) of not less than 5 and a CRE (=Cr+1.5Mo+2N+Cu (mass %)) of not less than 27.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to high-nitrogen austenitic stainlesssteel and, more specifically, high-nitrogen austenitic stainless steelwhich is excellent in seawater corrosion resistance and strength, andnonmagnetic.

2.Description of the Related Art

Austenitic stainless steel is generally excellent in corrosionresistance, but may cause corrosion depending on its using environment.For example, it is known that, when austenitic stainless steel is dippedin a halide aqueous solution, the passive film is broken by a halogenion such as Cl₋ or Br₋, causing local corrosion (pitting, crevicecorrosion). For prevention of such a local corrosion, the following areknown to be effective:

-   (1) Strengthening of passive film by increasing the amount of Cr-   (2) Reduction of active dissolution by addition of Mo, increase in    amount of Ni, or the like-   (3) Addition of N.

Therefore, for application in seawater or in marine environment,materials described below, for example, have been used, or uses thereofhave been examined:

-   (1) Austenitic stainless steel improved in corrosion resistance by    addition of Cr and/or Mo (e.g., SUS316)-   (2) Duplex stainless steel rich in Cr and Mo which are effective for    corrosion resistance and adjusted in components so that the ratio of    austenite phase is about 50% (e.g., SUS329J1, SUS329J4L, etc.)-   (3) Austenitic stainless steel largely increased in amounts of Cr    and Mo, with Cr(wt %)+3Mo(wt %)+10N (wt %)>38 (so-called super    stainless steel, e.g., SUS836L)-   (4) Ni-based alloy (e.g., Hastelloy-C276, Inconel 625, etc.)-   (5) Ti alloy.

The super stainless steel is excellent in seawater corrosion resistance,however, it is hard to say that it has sufficient strength. On the otherhand, the application of Ni-based alloy and Ti alloy has also beenexamined for a portion requiring strength and corrosion resistance,however, the Ni-based alloy and Ti alloy are expensive and of excessivequality. Accordingly, development of inexpensive and reliable stainlesssteel is requested, and various proposals have been conventionally made.

For example, there is disclosed in Patent Reference 1 (Japanese PatentApplication Laid-Open No. 10-183303), an austenitic steel alloy,containing 17.5% Cr-4% Mo-11% Mn-0.02% C-0.88% N-0.01% Ni, and thebalance Fe; and an austenitic steel alloy, containing 14% Cr-6% Mo-12%Mn-0.9% N, and the balance Fe. It is described inx the same referencethat corrosion resistance as high as that of super austenite can beensured by adopting such a composition.

Further, there is disclosed in Patent Reference 2 (Japanese PatentApplication Laid-Open No. 2000-309857) a stainless steel, containingC:0.003-0.012 wt %, Cr:15.08-25.02 wt %, Mn:0.01-0.16 wt %, Mo:1.03-9.21wt %, Ni:2.05-23.41 wt %, N:0.31-1.45 wt %, and the balance Fe, andhaving a pitting resistance equivalent PRE(=Cr (wt %)+3Mo (wt %)+10N (wt%)) which satisfies a predetermined relation with an area ratio (A %) ofnonmetallic inclusion and a diameter (D μm) thereof. It is described inthe same reference that, when the area ratio of nonmetallic inclusionand the diameter thereof are certain values or less, then reduction incorrosion resistance which is resulted from that the nonmetallicinclusion becomes coating defect of the passive film can be suppressed.

Further, there is disclosed in Patent Reference 3 (Japanese PatentApplication Laid-Open No. 2002-235153) a high-strength, high-corrosiveresistance nonmagnetic stainless steel, containing C: not more than0.15%, Si: not more than 1.0%, Mn:3.0-12.0%, P: not more than 0.030%,Ni: not more than 0.50%, Cr:15.0-21.0%, N:0.70-1.50%, Al: not more than0.020%, O: not more than 0.020%, and the balance Fe. It is described inthe same reference that Ni allergy resulted from elution of Ni can besuppressed by controlling the amount of Ni to not more than 0.5%;increased strength and nonmagnetic property can be attained byincreasing the amount of N instead of Ni; and excellent corrosionresistance can be ensured by reducing the amount of Mn.

-   [Patent Reference 1] Japanese Patent Application Laid-Open No.    10-183303-   [Patent Reference 2] Japanese Patent Application Laid-Open No.    2000-309857-   [Patent Reference 3] Japanese Patent Application Laid-Open No.    2002-235153

In the austenitic steel alloy disclosed in Patent Reference 1, 11-12% ofMn is added in order to enhance the nitrogen solbility. However, it ishard to say that adaptation of such a composition with high Mn canprovide sufficient corrosion resistance (particularly, pittingresistance) in seawater.

In the stainless steel disclosed in Patent Reference 2, Mn is hardlyadded, in order to enhance the corrosion resistance in seawater, whileNi is further added. However, in such a component range for perfectlydissolving Cr nitrides which are harmful to seawater corrosionresistance, solution treatment at an extremely high temperature isneeded. Solution treatment at a temperature exceeding 1250° C. isdisadvantageous for actual manufacture of a product in respect of graincoarsening and increase in manufacturing cost. Further, non-dissolved Crnitrides may be left depending on temperature restrictions on existingsolution treatment facilities, and sufficient seawater corrosionresistance cannot be obtained.

On the other hand, the high-strength, high-corrosion resistantnonmagnetic stainless steel disclosed in Patent Reference 3 is improvedin corrosion resistance because a large amount of N is included, and theamount of Mn is suppressed; and has properly high strength. Further,this stainless steel can be used also for accessories, biomedicalimplants and the like, because it is nonmagnetic and safe for humanbody. However, further improvement in strength and corrosion resistanceis demanded for the use in more severe conditions.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a high-nitrogenaustenitic stainless steel having seawater corrosion resistance as highas that of austenitic super stainless steel and strength as high as thatof duplex stainless steel.

Another object of the present invention is to provide a high-nitrogenaustenitic stainless steel capable of reducing Cr nitrides which areharmful to corrosion resistance without increasing the manufacturingcost by performing solution treatment in a practical temperature rangeof from 1050 to 1250° C.

A further object of the present invention is to provide a high-nitrogenaustenitic stainless steel having strength equal to or more than that ofNi-based alloy or Ti-based alloy by performing cold working to such ahigh-nitrogen austenitic stainless steel.

Further, an additional object of the present invention is to provide ahigh-nitrogen austenitic stainless steel which is nonmagnetic.

In order to overcome the above-mentioned problems, the high-nitrogenaustenitic stainless steel according to the present invention comprises:

0.005 mass %≦C≦0.25 mass %;

15.0 mass %≦Cr≦35.0 mass %;

0.2 mass %<Mn<10.0 mass %;

0.05 mass %≦Mo≦8.0 mass %;

0.01 mass %≦Cu≦4.0 mass %;

0.01 mass %≦Ni<5.0 mass %;

0.8 mass %<N≦1.8 mass %;

Si≦2.0 mass %;

P≦0.03 mass %;

S≦0.05 mass %;

Al≦0.030 mass %;

O≦0.020 mass %; and

the balance substantially containing Fe and impurities, and having:

PRE represented by the equation (1) and of not less than 5,PRE=(Cr+3.3Mo+16N)/Mn(mass %)  (1)and

CRE represented by the equation (2) and of not less than 27,CRE=Cr+1.5Mo+2N+Cu(mass %)  (2).

In this case, the high-nitrogen austenitic stainless steel preferablyhas a composition which can make the diameter of Cr nitrides to not morethan 2 μm by the solution treatment of 1050 to 1250° C.

The high-nitrogen austenitic stainless steel preferably has an index ofstability of austenitic phase: Ni_(eq)−Cr_(eq) of not less than 0,whereinNi_(eq)=Ni+Co+0.5Mn+0.3Cu+25N+30CCr_(eq)=Cr+2Si+1.5Mo+5V+5.5Al+1.75Nb+1.5Ti+0.75W.

When the content of each component element is optimized so that the PREand the CRE are within predetermined ranges, high strength can beobtained in addition to improvement in seawater corrosion resistance.The optimization of the content of each component element enablesdissolution of Cr nitrides with diameter of not less than 2 μm by thesolution treatment of 1050 to 1250C. When the content of each componentis optimized so that the index of stability of austenite phase:Ni_(eq)−Cr_(eq) is not less than 0, high-nitrogen austenitic stainlesssteel which is nonmagnetic even after strong cold working can beobtained. Further, when the high-nitrogen austenitic stainless steelhaving such a component is subjected to cold working, high strengthequal to or more than that of Ni-based alloy or Ti-based alloy can beobtained.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a view schematically showing a crevice forming tool; and

FIG. 1B is a view schematically showing a test piece with the creviceforming tool fixed thereto.

DETAILED DESCRIPTION OF THE INVENTION

One embodiment of the present invention will be then described indetail.

The high-nitrogen austenitic stainless steel according to the presentinvention includes elements described below, and the balancesubstantially containing Fe and inevitable impurities. The kinds andcomponent ranges of additive elements and the limitation reasons thereofare as follows.

In this specification, “mass %” means “mass percent,” which is definedby the equation (A):(mass %)=(amount of each element/total amount of all elements of steelor alloy etc.)×100  (A).

Further, “MPa” is a unit, and 1 MPa equals to 1×10⁶ N/m².

(1) 0.005 mass %≦C≦0.25 mass %

C is an austenite forming element, which is contributable tostabilization of austenite phase and effective for suppression ofnitrogen blow. It also contributes to improvement in strength because itis an interstitial element. On the other hand, addition of C exceeding0.25 mass % reduces the solubility of N, and also reduces dissolved-Crin a base phase by formation of Cr carbides, causing deterioration ofcorrosion resistance. Therefore, the addition amount of C is setpreferably to from not less than 0.005 mass % to not more than 0.25 mass%, more preferably to from not less than 0.005 mass % to not more than0.20 mass %, and even more preferably to from not less than 0.01 mass %to not more than 0.15 mass %.

(2) 15.0 mass %≦Cr≦35.0 mass %

Cr remarkably increases the solubility of N, thus, it is not onlyeffective for suppression of nitrogen blow but also largelycontributable to improvement in corrosion resistance and strength.Namely, Cr is an important element. Cr is a ferrite forming element,therefore, excessive addition thereof makes austenite phase unstable, sothat nonmagnetic property cannot be kept. Further, the residual amountof non-dissolved Cr nitrides in solution treatment is increased, causingremarkable reduction in corrosion resistance. Further, precipitation ofσ-phase which causes deterioration of toughness and ductility ispromoted. Therefore, the addition amount of Cr is set preferably to fromnot less than 15.0 mass % to not more than 35.0 mass %, more preferablyto from more than 21.0 mass % to not more than 32.0 mass %, and evenmore preferably to from more than 24.0 mass % to not more than 30.0 mass%.

(3) 0.2 mass %<Mn<10.0 mass %

Mn is an austenite forming element, which contributes to stabilizationof austenite phase. It remarkably increases the solubility of N,therefore, it is effective for suppression of nitrogen blow. Further, itreduces the temperature at which below-mentioned Cr nitride dissolves.It is effective also as a deoxidizing or desulfurizing element. On theother hand, excessive addition of Mn causes deterioration of pittingresistance. Therefore, the addition amount of Mn is set preferably tofrom more than 0.2 mass % to less than 10.0 mass %, more preferably tofrom more than 0.2 mass % to not more than 8.0 mass %, and even morepreferably to from not less than 2.0 mass % to not more than 7.0 mass %.

(4) 0.05 mass %≦Mo≦8.0 mass %

Mo increases the solubility of N and remarkably improves corrosionresistance. It also improves strength as a solid-solution strengtheningelement. On the other hand, excessive addition of Mo makes austenitephase unstable, inducing N blow, and also makes it difficult to ensurethe nonmagnetic property. Further, the excessive addition causesformation of a brittle phase and it causes reduction in toughness andductility, these are also detrimental to forging. Further, the amount ofnon-dissolved Cr nitrides in solution treatment is increased, causingremarkable reduction in corrosion resistance. Therefore, the additionamount of Mo is set preferably to from not less than 0.05 mass % to notmore than 8.0 mass %, more preferably to from not less than 0.05 mass %to not more than 2.5 mass %, and even more preferably to from not lessthan 0.10 mass % to less than 2.5 mass %.

(5) 0.01 mass %≦Cu≦4.0 mass %

Cu is an austenite forming element, which contributes to stabilizationof austenite phase. It also contributes to improvement in crevicecorrosion resistance. On the other hand, excessive addition of Cuincreases the amount of non-dissolved Cr nitrides in solution treatment,causing deterioration of corrosion resistance and reduction in hotworkability. Therefore, the addition amount of Cu is set preferably tofrom not less than 0.01 mass % to not more than 4.0 mass %, morepreferably to from not less than 0.02 mass % to not more than 2.0 mass%, and even more preferably to from not less than 0.05 mass % to notmore than 1.5 mass %.

(6) 0.01 mass %≦Ni<5.0 mass %

Ni is an austenite forming element, which contributes to stabilizationof austenite phase. On the other hand, excessive addition of Niincreases the amount of non-dissolved Cr nitrides in solution treatment,causing deterioration of corrosion resistance. Therefore, the additionamount of Ni is set preferably to from not less than 0.01 mass % to lessthan 5.0 mass %, more preferably to from not less than 0.01 mass % toless than 3.0 mass %, and even more preferably to from more than 0.5mass % to less than 3.0 mass %.

(7) 0.8 mass %<N≦1.8 mass %

N is one of the most important elements in the present invention. N isan interstitial element, which is very effective for improvement instrength, for stabilization of austenite phase, and for improvement incorrosion resistance. On the other hand, excessive addition of N inducesgeneration of N blow and also makes a large amount of non-dissolved Crnitrides or large amounts of Ti, Nb, and V nitrides remain in steel insolution treatment, causing remarkable reduction in corrosionresistance. Therefore, the addition amount of N is set preferably tofrom more than 0.8 mass % to not more than 1.8 mass %, and morepreferably to from more than 0.8 mass % to not more than 1.5 mass %.

(8) Si≦2.0 mass %

Although Al is more effective than Si as a deoxidizing element forgeneral steel, excessive addition of Al in high-nitrogen steel causesformation of AlN which leads to remarkable reduction in corrosionresistance, toughness and ductility. Therefore, as an main deoxidizingelement, it is preferable to use Si with an essential element Mn. SinceSi is a ferrite forming element, excessive addition thereof makesaustenite phase unstable, inducing N blow, and also makes it difficultto ensure the nonmagnetic property. Further, the excessive addition isnot only detrimental to forging, but also it remarkably deteriorates thetoughness and ductility of steel. The residual amount of non-dissolvedCr nitrides after solution treatment is also increased, causingremarkable reduction in corrosion resistance. Therefore, the additionamount of Si is set preferably to not more than 2.0 mass %, morepreferably to from not less than 0.01 mass % to not more than 1.0 mass%, and even more preferably to from not less than 0.01 mass % to notmore than 0.50 mass %.

(9) P≦0.03 mass %

Excessive addition of P causes reduction in hot workability, grainboundary strength, toughness and ductility, while excessive reduction ofP causes a rise of manufacturing cost. Therefore, the content of P ispreferably set to not more than 0.03 mass %.

(10) S≦0.05 mass %

Although S is effective for improvement in machinability, excessiveaddition thereof causes reduction in hot workability and causesdeterioration of corrosion resistance by formation of MnS. On the otherhand, excessive reduction of S causes a rise of manufacturing cost.Therefore, the content of S is set preferably to not more than 0.05 mass%, and more preferably to not more than 0.01 mass %.

(11) Al≦0.030 mass %

Al is very effective as a deoxidizing element similarly to Si and Mn. Inthis steel, however, if the addition amount of Al is more than 0.03 mass%, formation of AlN progresses, causing remarkable reduction incorrosion resistance, toughness and ductility. Therefore, the additionamount of Al is set preferably to not more than 0.030 mass %, morepreferably to not more than 0.025 mass %, and even more preferably tonot more than 0.020 mass %.

(12) O≦0.020 mass %

Addition of 0 exceeding 0.020 mass % reduces the cleanliness of steel,causing remarkable deterioration of corrosion resistance. Therefore, thecontent of 0 is set preferably to not more than 0.020 mass %, morepreferably to not more than 0.015 mass %, and even more preferably tonot more than 0.010 mass %.

The high-nitrogen austenitic stainless steel according to the presentinvention is characterized in that PRE is not less than 5 and CRE is notless than 27, in addition to that various additive elements are withinthe above-mentioned ranges.

The “PRE” means a pitting resistance equivalent, which is a valuerepresented by the following equation (1). In the equation (1), N, Crand Mo are used as elements which improve the pitting resistance and Mnis used as element which deteriorates the pitting resistance.PRE =(Cr+3.3Mo+16N)/Mn(mass %)  (1)

When the PRE is not less than 5, a pitting resistance equal to or morethan that of super stainless steel (e.g., SUS836L) is obtained. The PREis more preferably not less than 7.

The “CRE” means a crevice corrosion resistance equivalent, which is avalue represented by the following equation (2). In the equation (2),Cr, Mo, N and Cu are used as elements which reduce a critical pH.CRE =Cr+l.5Mo+2N+Cu (mass %)  (2)

When the CRE is not less than 27, a crevice corrosion resistance equalto or more than that of super stainless steel (e.g., SUS836L) isobtained. The CRE is preferably not less than 30.

The high-nitrogen austenitic stainless steel according to the presentinvention may contain, further, one or more second additive elements asdescribed below, in addition to the various elements described above.The component range of each element and the limitation reason thereofare as follows.

(13) 0.01 mass %≦W≦8.0 mass %

W contributes to improvement in corrosion resistance similarly to Mo,and also contributes to improvement in strength as a solid-solutionstrengthening element. On the other hand, excessive addition of W causesreduction in toughness and ductility by formation of a brittle phasesimilarly to Mo, and is also detrimental to forging. The amount ofnon-dissolved Cr nitrides in solution treatment is also increased,causing remarkable reduction in corrosion resistance. Therefore, theaddition amount of W is set preferably to from not less than 0.01 mass %to not more than 8.0 mass %, and more preferably to from not less than0.05 mass % to not more than 1.5 mass %.

(14) 0.01 mass %≦Co≦5.0 mass %

Co contributes to improvement in corrosion resistance and to improvementin strength. On the other hand, excessive addition of Co leads to riseof cost, and it increases the amount of non-dissolved Cr nitrides insolution treatment, causing remarkable reduction in corrosionresistance. Therefore, the addition amount of Co is set preferably tofrom not less than 0.01 mass % to not more than 5.0 mass %, morepreferably to from not less than 0.05 mass % to not more than 4.5 mass%, and even more preferably to from not less than 0.1 mass % to not morethan 4.0 mass %.

The high-nitrogen austenitic stainless steel according to the presentinvention may further contain one or more third additive elements asdescribed below, in addition to the above-mentioned various elements orinstead of the above-mentioned second additive elements.

The component range of each element and the limitation reason thereofare as follows.

(15) 0.01 mass %≦Ti≦0.5 mass %

Ti bonds to C and/or N to contribute to improvement in strength and tograin refining. On the other hand, excessive addition of Ti makes largeamounts of oxides and/or nitrides remain in steel, causing reduction incorrosion resistance. It also reduces the effective amount of dissolvedN, causing reduction in strength. Therefore, the addition amount of Tiis set preferably to from not less than 0.01 mass % to not more than 0.5mass %, more preferably to from not less than 0.02 mass % to not morethan 0.4 mass %, and even more preferably to from not less than 0.03mass % to not more than 0.3 mass %.

(16) 0.01 mass %≦Nb≦0.5 mass %

Nb bonds to C and/or N similarly to Ti to contribute to improvement instrength and to grain refining. On the other hand, excessive addition ofNb makes large amounts of oxides and/or nitrides remain in steel,causing reduction in corrosion resistance. It also reduces the effectiveamount of dissolved N, causing reduction in strength. Therefore, theaddition amount of Nb is set preferably to from not less than 0.01 mass% to not more than 0.5 mass %, more preferably to from not less than0.02 mass % to not more than 0.4 mass %, and even more preferably tofrom not less than 0.03 mass % to not more than 0.3 mass %.

(17) 0.01 mass %≦V<1.0 mass %

V bonds to C and/or N similarly to Ti and Nb to contribute toimprovement in strength and to grain refining. On the other hand,excessive addition of V makes large amounts of oxides and/or nitridesremain in steel, causing reduction in corrosion resistance. It alsoreduces the effective amount of dissolved N, causing reduction instrength. Therefore, the addition amount of V is set preferably to fromnot less than 0.01 mass % to less than 1.0 mass %, more preferably tofrom not less than 0.02 mass % to not more than 0.9 mass %, and evenmore preferably to from not less than 0.03 mass % to not more than 0.8mass %.

(18) 0.01 mass %≦Ta≦0.5 mass %

Ta bonds to C and/or N similarly to Ti, Nb and V to contribute toimprovement in strength and to grain refining. On the other hand,excessive addition of Ta makes large amounts of oxides and/or nitridesremain in steel, causing reduction in corrosion resistance. It alsoreduces the effective amount of dissolved N, causing reduction instrength. Therefore, the addition amount of Ta is set preferably to fromnot less than 0.01 mass % to not more than 0.5 mass %, more preferablyto from not less than 0.02 mass % to not more than 0.4 mass %, and evenmore preferably to from not less than 0.03 mass % to not more than 0.3mass %.

(19) 0.01 mass %≦Zr≦0.5 mass %

Zr contributes to improvement in strength. On the other hand, excessiveaddition of Zr leads to reduction in toughness and ductility. Therefore,the addition amount of Zr is set preferably to from not less than 0.01mass % to not more than 0.5 mass %, more preferably to from not lessthan 0.03 mass % to not more than 0.4 mass %, and even more preferablyto from not less than 0.05 mass % to not more than 0.3 mass %.

The high-nitrogen austenitic stainless steel according to the presentinvention may further contain one or more fourth additive elements asdescribed below, in addition to the above-mentioned various elements orinstead of the above-mentioned second and/or third additive elements.The component range of each element and the limitation reason thereofare as follows.

(20) 0.001 mass %≦B≦0.01 mass %

B is effective for improvement in strength and for improvement in hotworkability. On the other hand, excessive addition of B rather impairsthe hot workability, and deteriorates corrosion resistance. Therefore,the addition amount of B is set preferably to from not less than 0.001mass % to not more than 0.01 mass %, more preferably to from not lessthan 0.001 mass % to not more than 0.008 mass %, and even morepreferably to from not less than 0.001 mass % to not more than 0.005mass %.

(21) 0.001 mass %≦Ca≦0.01 mass %

(22) 0.001 mass %≦Mg≦0.01 mass %

Ca and Mg are effective for improving hot workability. Ca is alsoeffective for improving machinability. On the other hand, excessiveaddition of

Ca and Mg rather impairs the hot workability. Therefore, the additionamounts of Ca and Mg are set, respectively, preferably to not less than0.001 mass % to not more than 0.01 mass %, more preferably to from notless than 0.001 mass % to not more than 0.008 mass %, and even morepreferably to from not less than 0.001 mass % to not more than 0.005mass %.

The high-nitrogen austenitic stainless steel according to the presentinvention may further contain one or more fifth additive elements asdescribed below, in addition to the above-mentioned various elements, orinstead of the above-mentioned second, third and/or fourth additiveelements. The component range of each element and the limitation reasonthereof are as follows.

(23) 0.005 mass %≦Te≦0.05 mass %

Te contributes to improvement in machinability.

On the other hand, excessive addition of Te deteriorates corrosionresistance, toughness, ductility, and hot workability. Therefore, theaddition amount of Te is set preferably to from not less than 0.005 mass% to not more than 0.05 mass %, and more preferably to from not lessthan 0.01 mass % to not more than 0.04 mass %.

(24) 0.01 mass %≦Se≦0.20 mass %

Se contributes to improvement in machinability. On the other hand,excessive addition of Se deteriorates corrosion resistance, toughness,ductility, and hot workability. Therefore, the addition amount of Se isset preferably to from not less than 0.01 mass % to not more than 0.20mass %, more preferably to from not less than 0.02 mass % to not morethan 0.18 mass %, and even more preferably to from not less than 0.05mass % to not more than 0.15 mass %.

In the high-nitrogen austenitic stainless steel according to the presentinvention, it is desirable that Ni_(eq)−Cr_(eq) is not less than 0 inaddition that the additive elements are within the above-mentionedranges.

The “Ni_(eq)−Cr_(eq) ” means an index of stability of austenite phase,which is represented by using contents of main austenite formingelements and contents of main ferrite forming elements. The “Ni_(eq)”and the “Cr_(eq)” mean values represented by the following equations,respectively.Ni_(eq)=Ni+Co+0.5Mn+0.3Cu+25N+30CCr_(eq)=Cr+2Si+1.5Mo+5V+5.5Al+l.75Nb+1.5Ti+0.75W.

When the Ni_(eq)−Cr_(eq) is not less than 0, the austenite phase can bestably kept even after strong cold working.

Further, it is preferable that the high-nitrogen austenitic stainlesssteel according to the present invention has, particularly, acomposition which can make the diameter of Cr nitrides to not more than2 μm by solution treatment of 1050 to 1250° C. among the above-mentionedcompositions.

The high-nitrogen austenitic stainless steel according to the presentinvention is subjected, after forging or rolling, to solution treatmentfor 0.1 to 2 hours at such a heat treatment temperature as to besuitable for the composition of steel for the purpose of ensuringcorrosion resistance. The solution treatment is carried out in order todissolve Cr nitrides and to uniform microstructure. In this case,extinguishment of Cr nitrides with diameter exceeding 2 μm cannot alwaysbe attained in steel having any composition by performing solutiontreatment at a fixed temperature. Therefore, it is necessary to selectan optimum solution treatment temperature according to the compositionof the steel.

When the solution treatment temperature is excessively low,non-dissolved Cr nitrides with diameter exceeding 2 μm are generallyleft after solution treatment. Rough Cr nitrides cause reduction inseawater corrosion resistance. On the other hand, an excessively highsolution-treatment temperature causes grain coarsening and/or increasein facility cost.

In order to suppress the grain coarsening and/or the increase infacility cost while ensuring excellent seawater corrosion resistance,among the above-mentioned compositions, a composition which can make thediameter of non-dissolved Cr nitrides to not more than 2 μm by solutiontreatment of 1050 to 1250° C. is particularly preferred.

The effect of the high-nitrogen austenitic stainless steel according tothe present invention will be then described.

The high-nitrogen austenitic stainless steel of the present invention issuch that a large amount of N is dissolved to make elements such as Cr,Mn, Mo, Ni, Cu and the like to be proper, and the content of eachcomponent element is optimized so that the pitting resistance equivalentPRE and the crevice corrosion resistance equivalent CRE are withinpredetermined ranges. Therefore, seawater corrosion resistance as highas that of austenitic super stainless steel and high strength equivalentto that of duplex stainless steel are obtained.

When the addition amount of each component element is optimized, roughCr nitrides harmful to corrosion resistance can be reduced by solutiontreatment in a practical temperature range of 1050 to 1250° C. Since thesolution treatment can be performed at a relatively low temperature,increase in manufacturing cost can be suppressed.

When the content of each component element is optimized so that theindex of stability of austenite phase: Ni_(eq)−Cr_(eq) is not less than0, the austenite phase can be stably kept even after strong coldworking. Therefore, high-nitrogen austenitic stainless steel which isnonmagnetic can be obtained.

Further, when the content of each component element is optimized, and Crnitrides with diameter of 2 μm or more are dissolved by solutiontreatment of 1050 to 1250° C., the tensile strength after solutiontreatment becomes 1000 MPa or more by solid-solution strengthening of N.

When the content of each component element is optimized, Cr nitrideswith diameter of 2 μm or more are dissolved by solution treatment of1050 to 1250° C., and cold working is performed, then the tensilestrength after solution treatment and cold working is increased bysolid-solution strengthening and work hardening by N, and high strengthequivalent to or more than that of Ni-based alloy or Ti-based alloy canbe obtained.

Further, the strength after cold working rises in accordance with areduction ratio. Therefore, if the cold working condition is optimized,the tensile strength after solution treatment and cold working becomes1800 MPa or more.

Further, when the content of each component element is optimized, Crnitrides with diameter of 2 μm or more are dissolved by solutiontreatment of 1050 to 1250° C., and the cold working condition isoptimized, then the tensile strength after solution treatment and coldworking becomes 2000 MPa or more by solid-solution strengthening andwork hardening by N. Even in such a high strength state, an elongationof not less than 10% can be ensured.

EXAMPLES Examples 1 to 18 and Comparative Examples 1 to 23

[1. Preparation of Samples]

Each of alloys having chemical components shown in Tables 1 and 2 wasmelted and cast in a pressurized induction furnace, whereby 50 kg ofingot was obtained. The ingot was homogenized, and made to a round barwith φ24 by hot forging. The resulting round bar was subjected tosolution treatment. As the solution treatment condition, the bar washeld at 1050 to 1300° C. for 1 hour, and then cooled with water.

The same test was carried out with respect to super stainless steel:SUS836L (Comparative Example 14), duplex stainless steel: SUS329J4L(Comparative Example 15), austenitic stainless steel: SUS316(Comparative Example 16), Ni-based alloy: Inconel 625 (ComparativeExample 17), and Ti (Comparative Example 18) as representatives ofexisting steel products. The heat treatment was performed in a generallyadapted temperature condition. TABLE 1 C Si Mn P S Cu Ni Cr Mo Co W V AlTi EXAMPLES 1 0.03 0.13 0.4 0.01 0.01 0.16 0.48 27.3 1.30 0.008 2 0.030.21 1.8 0.02 0.01 0.05 0.20 24.9 1.90 0.23 0.12 0.007 3 0.08 0.31 7.90.02 0.01 0.23 2.30 31.4 0.92 0.06 0.006 4 0.03 0.20 4.2 0.01 0.01 0.720.50 17.9 5.80 0.26 0.13 0.006 0.09 5 0.02 0.11 3.4 0.02 0.01 0.32 1.3821.2 6.43 0.73 0.005 0.06 6 0.03 0.22 6.5 0.02 0.01 0.16 0.07 27.1 0.210.47 0.15 0.005 7 0.05 0.21 7.3 0.02 0.01 0.16 0.09 25.0 2.30 0.32 0.230.006 0.02 8 0.03 0.15 7.7 0.02 0.01 0.43 0.03 21.2 2.43 0.007 9 0.060.02 9.1 0.02 0.01 0.19 0.09 19.5 3.90 0.07 0.008 10 0.22 0.22 7.1 0.020.01 0.16 0.07 24.3 3.80 0.47 0.15 0.005 11 0.05 0.21 5.8 0.02 0.01 1.390.09 23.7 1.75 0.006 12 0.06 0.20 5.9 0.02 0.01 0.16 3.80 23.3 3.40 0.050.005 13 0.04 0.20 7.2 0.02 0.01 0.16 0.22 24.1 2.40 2.10 0.15 0.005 140.04 0.20 5.4 0.02 0.01 0.16 0.18 25.3 1.74 0.28 1.44 0.005 0.15 15 0.010.28 6.9 0.01 0.01 0.16 0.22 25.0 2.48 0.011 16 0.03 0.01 7.8 0.02 0.010.16 0.10 24.3 2.10 0.15 0.007 17 0.07 0.31 4.5 0.01 0.01 0.13 1.01 23.24.20 0.006 18 0.05 0.18 8.8 0.01 0.01 0.13 0.05 24.4 2.33 0.005 19 0.040.20 5.4 0.02 0.01 0.63 2.20 24.6 1.80 0.005 20 0.08 0.28 6.9 0.01 0.010.16 1.30 25.0 2.45 0.009 21 0.03 0.15 8.4 0.02 0.01 0.20 1.10 24.3 2.300.007 22 0.09 0.31 6.8 0.01 0.01 0.13 1.01 22.1 4.20 0.006 23 0.05 0.184.5 0.01 0.01 0.51 2.40 24.4 2.33 0.005 COMPARATIVE 1 0.03 0.16 1.5 0.020.01 0.52 0.16 24.2 1.94 0.15 0.05 0.010 EXAMPLES 2 0.07 0.21 4.0 0.020.01 0.15 0.17 22.2 3.90 0.51 0.31 0.055 3 0.05 0.20 6.0 0.01 0.01 0.150.07 19.2 12.90 0.11 0.008 0.05 4 0.05 2.44 8.0 0.02 0.01 0.19 0.20 37.20.51 0.009 5 0.04 0.12 0.1 0.02 0.01 0.21 6.20 27.3 0.56 0.05 0.05 0.0076 0.05 0.14 8.0 0.02 0.01 4.60 0.10 23.2 0.98 0.009 7 0.04 0.19 12.80.02 0.01 0.14 0.16 13.0 7.99 0.40 0.009 8 0.06 0.17 9.7 0.01 0.01 0.160.06 23.3 1.54 0.15 0.008 0.03 9 0.33 0.24 4.0 0.01 0.01 0.14 0.31 26.80.54 0.19 0.006 10 0.08 0.23 1.2 0.01 0.01 0.14 0.24 29.0 1.01 0.0090.03 11 0.02 0.32 9.2 0.01 0.01 0.13 0.06 18.3 2.21 0.005 12 0.02 0.1717.6 0.01 0.01 0.23 0.31 18.4 2.12 0.007 13 0.07 0.15 13.0 0.01 0.010.20 0.01 17.8 2.02 0.012 14 0.02 0.17 0.8 0.02 0.01 0.92 25.1 19.9 6.220.009 15 0.02 0.21 0.9 0.02 0.01 6.4 24.9 3.98 0.010 16 0.04 0.34 1.10.03 0.01 0.15 11.8 17.5 2.12 0.025 17 0.05 0.31 0.1 0.03 0.01 Bal. 22.19.10 0.011 18 0.01 Bal.

TABLE 2 Nieq- Nb O N B Mg Ca Ta Zr Te Se PRE CRE Creq EXAMPLES 1 0.0021.31 131.4 32.0 4.8 2 0.05 0.003 1.47 0.005 30.4 30.7 10.6 3 0.002 1.330.003 7.1 35.7 8.2 4 0.04 0.002 1.21 13.4 29.7 6.9 5 0.002 1.22 0.0030.002 0.09 0.10 0.03 0.10 18.2 33.6 3.8 6 0.001 1.20 7.2 30.0 6.7 7 0.010.003 1.24 0.006 7.2 31.1 7.5 8 0.002 0.93 0.002 0.003 5.7 27.1 3.0 90.001 0.83 5.0 27.2 1.5 10 0.001 1.08 0.003 7.6 32.3 7.2 11 0.003 1.180.007 8.3 30.1 7.6 12 0.003 1.26 0.002 0.003 9.3 31.1 11.2 13 0.05 0.0031.08 0.06 6.8 30.0 5.2 14 0.05 0.003 1.06 0.09 8.9 30.0 1.2 15 0.070.002 1.26 0.03 7.7 31.4 6.1 16 0.005 0.94 0.003 0.006 5.9 29.5 0.8 170.004 1.15 12.3 31.9 4.0 18 0.003 1.07 5.6 30.2 4.5 19 0.005 1.14 9.030.2 7.1 20 0.007 1.10 7.3 31.0 5.4 21 0.005 1.07 5.8 30.1 4.9 22 0.0041.10 7.9 30.7 5.6 23 0.003 1.05 10.9 30.5 4.3 COMPARATIVE 1 0.029 1.200.003 0.11 33.2 30.0 4.6 EXAMPLES 2 0.002 1.03 0.11 0.09 12.9 30.3 0.3 30.003 1.19 0.002 0.003 0.10 13.5 41.1 −5.3 4 0.002 1.02 6.9 40.2 −11.6 50.003 1.26 0.11 0.02 0.10 448.3 30.9 10.6 6 0.005 1.21 0.003 5.7 31.712.2 7 0.05 0.002 1.21 0.030 0.004 4.6 27.5 10.6 8 0.05 0.004 0.69 4.127.2 −2.9 9 0.002 1.11 11.6 30.0 10.9 10 0.004 1.85 0.002 51.6 34.4 18.511 0.002 0.98 0.0024 0.003 4.5 23.7 7.5 12 0.03 1.02 0.12 2.4 23.9 13.313 0.003 1.01 3.1 23.1 12.7 14 0.007 0.14 56.9 30.4 0.1 15 0.004 0.1945.6 31.3 −19.1 16 0.005 0.03 22.7 20.9 −7.2 17 0.005 0.03 — — — 18 0.090.01 — — —[2.Evaluation (1)]

The resulting ingots and round bars were evaluated as follows.

(1) Existence of Nitrogen Blow:

A test piece was cut out from a bottom portion of each ingot, and visualconfirmation of nitrogen blow holes was performed therefor.

(2) Selection of the Solution Treatment Temperature:

The round bar after hot forging was subjected to solution treatment atvarious temperatures, after that, optional five visual fields thereofwere observed by an optical microscope at 400-fold. Thereby, the lowesttemperature at which the circle-converted diameter of Cr-based nitridesbecomes 2 μm or less was determined. This lowest temperature wasselected as the solution treatment temperature.

(3) Tensile Strength, Critical Pitting Temperature (CPT) andDepassivation pH:

A test piece was sampled from each round bar heat-treated at theselected solution treatment temperature, and a tensile strength, acritical pitting temperature (CPT) and a depassivation pH thereof weremeasured.

The tensile strength was measured in accordance with JIS Z2241. Thecritical pitting temperature (CPT) was measured in accordance with JISG0578.

Further, with respect to the depassivation pH, the test piece was dippedin a 4.9% NaCl aqueous solution the pH of which is adjusted with HCl. Aspontaneous potential thereof after the lapse of 24 hours was measured,the pH at the time when the potential transits from the active area tothe passive area was determined and taken as the depassivation pH. Thedepassivation pH is correlative with crevice corrosion resistance, andthe crevice corrosion resistance is more excellent as the depassivationpH is smaller.

The evaluation results of each sample are shown in Table 3.

In Comparative Examples 1, 2 and 9, the CPT was reduced, while thedepassivation pH was raised because of excessive 0, Al and C. InComparative Examples 3, 4 and 5, the solution treatment temperatureexceeded 1250° C. because of excessive Mo, Cr and Ni. In ComparativeExample 6, forging crack was caused because of excessive Cu. InComparative Examples 7 and 8, the CPT was reduced, while thedepassivation pH was raised because of excessive Mn and insufficient N.In Comparative Examples 11, 12 and 13, the CPT was reduced, or thedepassivation pH was raised because of low PRE or CRE. In ComparativeExample 10, N blow was caused in the ingot because of excessive N.

In contrast to this, in Examples 1 to 23, no N blow was caused. Thesolution treatment temperature was within the range of from 1050 to1250° C. Further, the tensile strength after solution treatment was 1000MPa or more in each case, and extremely satisfactory corrosionresistance was shown. The Ni_(eq)−Cr_(eq) was not less than 0 in eachcase. TABLE 3 Existence Solution treatment Tensile Depassivation ofN-blow (° C.) Strength (MPa) CPT (° C.) pH EXAMPLES 1 None 1250 1150 >70<0.5 2 None 1250 1240 >70 <0.5 3 None 1200 1189 >70 <0.5 4 None 11501150 >70 <0.5 5 None 1200 1171 >10 <0.5 6 None 1150 1130 >70 <0.5 7 None1150 1160 >70 <0.5 8 None 1100 1093 >70 0.60 9 None 1050 1072 >70 0.6010 None 1150 1102 >70 <0.5 11 None 1200 1141 >70 <0.5 12 None 12001170 >70 <0.5 13 None 1150 1141 >70 <0.5 14 None 1150 1131 >70 <0.5 15None 1150 1201 >70 <0.5 16 None 1100 1091 >70 <0.5 17 None 1200 1120 >70<0.5 18 None 1150 1008 >70 <0.5 19 None 1200 1106 >70 <0.5 20 None 11501102 >70 <0.5 21 None 1150 1114 >70 <0.5 22 None 1150 1133 >70 <0.5 23None 1200 1066 >70 <0.5 COMPARATIVE 1 None 1250 1144 52.5 1.03 EXAMPLES2 None 1200 1108 47.5 1.13 3 None 1300 1192 >70 <0.5 4 None 13001207 >70 <0.5 5 None 1300 1157 >70 <0.5 6 None Forging crack Forgingcrack Forging crack Forging crack 7 None 1200 1146 45 0.68 8 None 1100932 40 0.73 9 None 1250 1125 50 0.98 10 Occured — — — — 11 None 11501098 60 1.23 12 None 1100 1106 22.5 1.23 13 None 1100 1104 27.5 1.28 14None 1150 692 >70 <0.5 15 None 1100 702 42.5 <0.6 16 None 1100 599 51.30 17 None — 690 >70 <0.5 18 None — 420 >70 <0.5[3.Evaluation (2)]

With respect to Examples 5, 7, 15 and 16, 50 kg of each ingot washomogenized, and then made into a sheet stock 5 mm in thickness by hotforging and hot rolling. The solution treatment was then performedthereto at a solution treatment temperature selected in Evaluation (1).A test piece was cut out from the resulting sheet stock, and a crevicecorrosion dipping test in real seawater for one year was performed. Thesame test was carried out also with respect to Comparative examples 14,15, 16 and 18.

A crevice forming tool is shown in FIGS. 1A and 1B. The crevice formingtool 10 includes a cylindrical projection 12 having an outside diameterof 23 mm and an inside diameter of 20.5 mm at the tip thereof, as shownin FIG. 1A. The cylindrical projection 12 includes grooves 12 a having awidth of 1 mm and a depth of 0.5 mm so as to form a total of twentycrevice forming parts 12 b. Such a crevice forming tool 10 was fixed toboth sides of a test piece 14 by a Ti-made bolt 16 a and nut 16b, asshown in FIG. 1B. Namely, a total of forty crevices were formed per onetest piece. Three test pieces were suspended in a place 1 m below thesea level and dipped therein for one year. After the test was ended, thenumber of corroded crevices among a total of one hundred and twentycrevices was measured to determine a crevice corrosion generation rate.The result is shown in Table 4. TABLE 4 Crevice Corrosion Generationrate (%) Remarks Example 5 0 Example 7 0 Example 15 0 Example 16 0Comparative example 14 0 SUS836L Comparative example 15 8 SUS329J4LComparative example 16 62 SUS316 Comparative example 18 0 Ti

In Comparative Examples 15 (corresponding to SUS329J4L) and 16(corresponding to SUS316), the crevice corrosion generation rates were8% and 62%, respectively. In Examples 5, 7, 15 and 16, the crevicecorrosion generation rate was 0%, and the crevice corrosion resistanceswere equivalent to those in Comparative Examples 14 (corresponding toSUS836L) and 18 (Ti).

[4.Evaluation (3)]

For Examples 5, 7 and 15, 50 kg of each ingot was homogenized and madeinto a wire rod of φ12.5 by hot forging and hot rolling. Then, solutiontreatment was performed thereto at a solution treatment temperatureselected in Evaluation (1). Further, the wire rod was made into a wirerod of φ8.8 by cold working with a reduction ratio of 50%. A test piecewas cut out from the resulting wire rod, and a tensile strength and anelongation thereof were measured. The tensile strength and theelongation were measured in accordance with JIS Z2241. The results areshown in Table 5.

As is apparent from Table 5, each of the steel stocks has a tensilestrength after cold working of not less than 2000 MPa, and an elongationof not less than 10%. TABLE 5 Tensile strength Elongation after after50%-Cold working 50%-Cold working (MPa) (%) Example 5 2235 12.1 Example7 2254 11.0 Example 15 2273 10.2

The embodiment of the present invention was described above in detail,but the present invention is never limited to the above-mentionedembodiment, and various modifications can be made within the scope notdeviating from the gist of the present invention.

The high-nitrogen austenitic stainless steel according to the inventioncan be used in applications requiring seawater resistance, for example,for marine-related equipment, seashore environmental members, structuralmembers for marine structures, seawater-desalination plant members,seawater heat exchanger members, submarine cables, structural membersfor submarine structures, mooring ropes, aquaculture fish nets, bridgewires for seashore section, seawater pumps, shafts, fastening memberssuch as bolt, nut and screw, and the like.

This high-nitrogen austenitic stainless steel can be used also forgeneral high-strength, high-corrosive member such as bolts, nuts,cylinder liners, shafts, hubs, connectors, bearings, races, rails,gears, pins, screws, rolls, turbine blades, molds, dies, drills, valves,valve seats, cutters, nozzles, gaskets, rings, springs, industrialfurnace members, chemical plant members, medicine producing members,food producing plant members, food producing device members, oildrilling members, petroleum refining plant members, refuse incineratormembers, steam turbine members, gas turbine members, reactor members,aircraft members, biomass plant members, and the like.

Further, steel products reduced in content of Ni are particularlyapplicable to biological materials and accessories, and can be used, forexample, for:

-   (1) accessories such as necklaces, pierces or rings, back lids for    watches, watch bands, eyeglass frames, interdental brushes and the    like, which directly touch human bodies;-   (2) dental materials such as artificial roots and correction wires,    which are used within living bodies;-   (3) implant materials such as plates, bolts, nuts, springs, screws,    wires, electrodes, artificial bones, and artificial joints;-   (4) medical instruments such as injection needles, knives, surgical    knives, scissors, forceps, and drills.

Further, steel products sufficiently ensuring stability of austenitephase can be used as nonmagnetic, high-strength, and high-corrosiveresistance materials for:

-   (1) springs, shafts, bearings, races, pins, dies, and rails for    precision electronic parts;-   (2) wires and meshes for printed board manufacturing parts;-   (3) biological implant electrodes, MRI parts, and MRI-responding    biological implant members; and-   (4) medicine producing members, hanger members, linear motor car    members, semiconductor manufacturing device parts, pincettes,    bearing, scissors, cutters, and the like.

1. A high-nitrogen austenitic stainless steel, comprising: 0.005 mass%≦C≦0.25 mass %; 15.0 mass %≦Cr≦35.0 mass %; 0.2 mass %<Mn<10.0 mass %;0.05 mass %≦Mo≦8.0 mass %; 0.01 mass %≦Cu≦4.0 mass %; 0.01 mass %≦Ni<5.0mass %; 0.8 mass %<N≦1.8 mass %; Si≦2.0 mass %; P≦0.03 mass %; S≦0.05mass %; Al≦0.030 mass %; O≦0.020 mass %, and having: PRE represented byan equation (1) and of not less than 5,PRE=(Cr+3.3Mo+16N)/Mn(mass %)  (1) and CRE represented by an equation(2) and of not less than 27,CRE=Cr+1.5Mo+2N+Cu(mass %)  (2) and further optionally containing one ormore elements selected from the group consisting of: at least one of:0.01 mass %≦W≦8.0 mass %; and 0.01 mass %≦Co≦5.0 mass %; at least oneof: 0.01 mass %≦Ti≦0.5 mass %; 0.01 mass %≦Nb≦0.5 mass %; 0.01 mass%≦V<1.0 mass %; 0.01 mass %≦Ta≦0.5 mass %; and 0.01 mass %≦Zr≦0.5 mass%; at least one of: 0.001 mass %≦B≦0.01 mass %; 0.001 mass %≦Ca≦0.01mass %; and 0.001 mass %≦Mg≦0.01 mass %; at least one of: 0.005 mass%≦Te≦0.05 mass %; and 0.01 mass %≦Se≦0.20 mass %; and the balancesubstantially containing Fe and impurities.
 2. The high-nitrogenaustenitic stainless steel according to claim 1, wherein an index ofstability of austenite phase: Ni_(eq)−Cr_(eq) is not less than 0,whereinNi_(eq)=Ni+Co+0.5Mn+0.3Cu+25N+30CCr_(eq)=Cr+2Si+1.5Mo+5V+5.5Al+1.75Nb+1.5Ti+0.75W.
 3. The high-nitrogenaustenitic stainless steel according to claim 1 or 2, wherein tensilestrength in a solution-treated state is not less than 1000 MPa.
 4. Thehigh-nitrogen austenitic stainless steel according to claim 1 or 2,wherein tensile strength after solution treatment and cold working isnot less than 1800 MPa.
 5. The high-nitrogen austenitic stainless steelaccording to claim 1 or 2, wherein tensile strength after solutiontreatment and cold working is not less than 2000 MPa, and elongation isnot less than 10%.
 6. The high-nitrogen austenitic stainless steelaccording to claim 3, wherein tensile strength after solution treatmentand cold working is not less than 1800 MPa.
 7. The high-nitrogenaustenitic stainless steel according to claim 3, wherein tensilestrength after solution treatment and cold working is not less than 2000MPa, and elongation is not less than 10%.
 8. The high-nitrogenaustenitic stainless steel according to claim 4, wherein tensilestrength after solution treatment and cold working is not less than 2000MPa, and elongation is not less than 10%.
 9. The high-nitrogenaustenitic stainless steel according to claim 6, wherein tensilestrength after solution treatment and cold working is not less than 2000MPa, and elongation is not less than 10%.